GENETIC ANALYSES OF CERTAIN CHARACTERS IN COMMON WHEAT USING WHOLE CHROMOSOME SUBSTITUTION LINES

Abstract

Three sets of substitution lines of the spring wheat variety Chinese with chromosomes from the donor varieties Thatcher, Hope and Timstein were used to study the genetics of awning, earliness, lodging, plant height, spike density, 1000-kernel weight and yield. The various substitution lines, each representing a genotype that differs from that of the recipient variety only with respect to the genes carried by the substituted chromosome, were studied in replicated field trials so that environmental effects on the character in question could be easily removed by appropriate analysis. This permitted a comparison of the genetic effects of individual chromosomes against the standard based on the performance of a population of like genotypes.Genes conditioning awning were associated with seven chromosomes. Studies of earliness indicated that time of heading is conditioned by (a) major genes that differentiate spring and winter growth habit, and (b) genes that modify the expression of growth habit genes to a greater or lesser extent. Differences in spike density among the lines were due to minor genes only; the same was true for plant height. Lodging, protein content, 1000-kernel weight and yield were found to be conditioned by polymeric or multiple genes on many chromosomes; the effects of these individual genes though small were not usually equal.Where a substituted chromosome brings about a significant departure in character expression from that of the recipient variety, a method is outlined whereby the number of genes on a particular chromosome can be determined. The merits of the substitution method are discussed, and it is concluded that it is valuable, and gives a high degree of precision in genetic studies of polyploid organisms and that under certain conditions its effectiveness is similar to that of the backcross method for incorporating characters controlled by one or two genes into a given line or variety.